/**
 * Copyright 2013 David Rusek <dave dot rusek at gmail dot com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.robotninjas.barge.state;

import com.google.common.base.Predicate;
import com.google.common.util.concurrent.AbstractFuture;
import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;
import java.util.List;
import java.util.concurrent.locks.ReentrantLock;

import static com.google.common.base.Preconditions.checkNotNull;

@ThreadSafe
class MajorityCollector<T> extends AbstractFuture<Boolean> implements FutureCallback<T> {

    private final ReentrantLock lock = new ReentrantLock();
    private final Predicate<T> isSuccess;
    private final int totalNum;
    @GuardedBy("lock")
    private int numSuccess = 0;
    @GuardedBy("lock")
    private int numFailed = 0;

    private MajorityCollector(@Nonnegative int totalNum, @Nonnull Predicate<T> isSuccess) {
        this.totalNum = totalNum;
        this.isSuccess = isSuccess;
    }

    @Nonnull
    public static <U> ListenableFuture<Boolean> majorityResponse(@Nonnull List<ListenableFuture<U>> responses, @Nonnull Predicate<U> isSuccess) {
        MajorityCollector collector = new MajorityCollector(responses.size(), isSuccess);
        for (ListenableFuture<U> response : responses) {
            Futures.addCallback(response, collector);
        }
        return collector;
    }

    private void checkComplete() {
        if (!isDone()) {
            final double half = totalNum / 2.0;
            if (numSuccess >= half) {
                set(true);
            } else if (numFailed > half) {
                set(false);
            }
        }
    }

    @Override
    public void onSuccess(@Nonnull T result) {

        checkNotNull(result);

        lock.lock();
        try {
            if (isSuccess.apply(result)) {
                numSuccess++;
            } else {
                numFailed++;
            }
            checkComplete();
        } finally {
            lock.unlock();
        }

    }

    @Override
    public void onFailure(@Nonnull Throwable t) {
        lock.lock();
        try {
            numFailed++;
            checkComplete();
        } finally {
            lock.unlock();
        }
    }

}
